USMLE – Hyperthyroidism
Hyperthyroidism is the clinical syndrome which results from exposure of the body tissues to excess circulating levels of free thyroid hormones. It is a common disorder with a prevalence of about 20/1000 females; males are affected five times less frequently.
It is important to identify the cause of hyperthyroidism in order to prescribe appropriate treatment. In over 90% of patients hyperthyroidism is due to Graves’ disease, multinodular goiter or an autonomously functioning solitary thyroid nodule (toxic adenoma). Excess pituitary secretion of TSH which mayor may not originate from a tumor, intrinsic thyroid-stimulating activity of human chorionic gonadotrophin in hydatidiform mole and choriocarcinoma, ovarian teratoma containing thyroid tissue (struma ovarii), and metastatic differentiated carcinoma of the thyroid are extremely rare causes.
Hyperthyroidism usually develops insidiously and most patients have had symptoms for at least 6 months before presentation. There is great individual variation in the dominant features; for example, the initial presentation may be to a cardiologist on account of palpitations, to a dermatologist because of pruritus, or to a gastrointestinal clinic with diarrhea. Weight loss in older patients may be associated with anorexia, raising the possibility of carcinoma. Atrial fibrillation, which is seldom seen in young patients unless there is severe long-standing disease, is common in the elderly. In children, medical attention may be sought because of behavior disorders, deteriorating academic performance or a premature growth spurt.